TOKYO — A former US nuclear regulator says cleaning up Japan’s wrecked Fukushima plant is a bigger challenge than the work he led at Three Mile Island and that ongoing radioactive water leaks are a minor part of that task.

Lake Barrett was appointed this month by plant operator Tokyo Electric Power Co. as an outside adviser for the decades-long decommissioning process. He led the Three Mile Island accident cleanup for nearly a decade as part of the Nuclear Regulatory Commission.

He said that the meltdowns in three of the reactors, massive radiation leaks, and the volume of contaminated water at the Fukushima Daiichi plant, on Japan’s northeast coast, make it a more complicated cleanup.

Advertisement

‘‘In comparison to Three Mile Island, Fukushima is much more challenging, much more complex a job,’’ Barrett told a Tokyo news conference.

Compared to the magnitude of that task, the leakage problem is a ‘‘very low health impact and not a concern,’’ he told The Associated Press in an exclusive interview later Friday. The attention on the contaminated water leaks is ‘‘out of proportion,’’ and is hurting the overall cleanup process by slowing things down, he said.

The 1979 core melt accident at the Three Mile Island nuclear plant in Pennsylvania involved one reactor. All the radioactivity was contained in one building, where 8,000 tons of contaminated water were trapped.

In Fukushima, the catastrophe was precipitated by a massive earthquake and tsunami, whose aftermath are further adding to the difficulties of containing and cleaning up after the meltdowns of the three reactors. Moreover, buildings at the Japanese plant were destroyed or damaged by hydrogen explosions, which released massive radioactive elements into the air and sea.

But despite worries over the massive quantities of water needed to cool the reactors, the risk of radiation-contaminated water to public health is minimal, Barrett said.